Partial oxidation or water vapor reforming, which uses oil or natural gas as a raw material, generates a lot of carbon dioxide gas at the time of hydrogen synthesis. Therefore, a UT-3 cycle using solar heat, and a method disclosed by Japanese Patent Publication No. 07-267601 are proposed as a method that does not generate a carbon dioxide gas. However, this method requires a large-scale system in order to use solar heat, and also the cost of the large-scale system becomes very high.
Additionally, many proposals using a hydrogen storing alloy are made as means for safely storing/carrying hydrogen instead of a high-pressure steel bottle. However, there are problems that a high hydrogen pressure is required to make a hydrogen storing alloy occlude hydrogen, and the hydrogen storing alloy cannot be used in an atmosphere of air and water vapor, which costs very high.
For a fuel cell using hydrogen and air as raw materials, a method supplying hydrogen with methanol or gasoline steam reforming is general, and a number of inventions are made. With these methods, however, carbon monoxide and a carbon dioxide gas occur simultaneously. Especially, for carbon monoxide, a device for reducing carbon monoxide to 10 ppm or less is required due to a problem that an electrode of a fuel cell is poisoned, which leads to a high cost.
As a method producing hydrogen from water, a steam iron method is known. This method is a method using oxidation-reduction (Fe→FeO(Fe3O4)→Fe) of only iron as a reaction. For the reaction, a temperature, by way of example, equal to or higher than 600° C. is required. If oxidation-reduction is repeated, there is a disadvantage that so-called sintering which agglomerates metallic iron occurs, and the activity of the metallic iron is rapidly degraded. Accordingly, a hydrogen generating medium (oxidation-reduction material) which does not make a sintering phenomenon occur, is superior in resistance, and exhibits high activity is demanded.